Sheldon Aaronson. Cambridge World History of Food. Editor: Kenneth F Kiple & Kriemhild Conee Ornelas. Volume 1. Cambridge, United Kingdom: Cambridge University Press, 2000.
Fungi are uninucleate or multinucleate, eukaryotic organisms with nuclei scattered in a walled and often septate mycelium (the vegetative part of a fungus). Nutrition is heterotrophic (at least one or more organic molecules required), and fungi usually obtain their nutrients by way of diffusion or active transport. They lack chlorophyll but may have other pigments such as carotenoids, flavonoids, and so forth.
The true fungi, Eumycota, are grouped into five divisions:
- Mastigomycotina (aquatic or zoospore-producing fungi) – unicellular or mycelial (coenocytic, no intercellular walls); motile, uni- or biflagellate zoospores during life cycle.
- Zygomycotina – coenocytic mycelium; sexual state (teleomorph) spores are zygospores which may be absent; asexual state (anamorph) is predominant stage consisting of uni- or multispored sporangia.
- Ascomycotina – mycelium unicellular to multicellular; regularly septate; asexual state often present; sexual state spores are ascospores formed inside an ascus (sac); no motile state.
- Basidiomycotina – mycelium unicellular to multicellular, regularly septate; conidial asexual state common; sexual state and motile cells absent.
- Deuteromycotina – unicellular to multicellular mycelia; regularly septate; conidial asexual state common; no sexual state; no motile cells (O’Don-nell and Peterson 1992).
D. L. Hawksworth, B. C. Sutton, and G.A. Ainsworth (1983) have estimated that there are about 250,000 species of fungi, of which Mastigomycotina composes 1.8 percent, Zygomycotina 1.2 percent, Ascomycotina about 45 percent, Basidiomycotina about 25.2 percent, and Deuteromycotina about 26.8 percent.
Most edible fungi belong to divisions 2 to 5, just listed. Yeasts are single-celled fungi that reproduce asexually by budding or fission, or sexually through ascospore formation. The term “mushroom” refers to those macrofungi (visible to the naked eye) with edible fruiting bodies (sporophores), whereas “toadstool” refers to macrofungi with toxic fruiting bodies; both mushrooms and toadstools are found in more than one of the fungal divisions (Hawksworth et al. 1983; Koivikko and Savolainen 1988).
Fungi have been associated with humans since prehistoric times and must have been collected and eaten along with other plants by hunter-gatherers prior to the development of agriculture (Oakley 1962; Monthoux and Lündstrom-Baudois 1979; Pöder, Peintner, and Pümpel 1992). Although their prehistoric use remains uncertain, they may have been employed as food, in the preparation of beverages, and as medicine.
There is, however, no specific evidence for the use of fungi prior to the Neolithic period, when fungi consumption would have been associated with the drinking of mead (yeast-fermented diluted honey) and yeast-fermented beer or wine, and, somewhat later, the eating of yeast-fermented (leavened) bread.
Beer was the preferred fermented drink of the Sumerians of the Late Uruk period dating to the late fourth millennium B.C. R. H. Michel, P. E. McGovern, and V. R. Badler (1992) have noted the similarity of the grooves on a Late Uruk jar at Godin Tepe (in the Zagros Mountains of Iran) with the Sumerian sign for beer, kas. The grooves contained a pale yellow residue, which the authors thought was an oxalate salt – oxalate salts are the principal molecules in “beerstone,” a material found on barley beer fermentation containers. The Sumerians were very fond of beer and brewed at least 19 different kinds. They also used beer in some of their medical prescriptions (Majno 1975). Date and grape wine were known in Babylonia by 2900 B.C. (Saggs 1962).
Fungi were eaten or drunk, perhaps unwittingly, in Egypt thousands of years ago, in beer and, later, in wine and bread.Yeasts were discovered in a vase of the Late Predynastic period (3650-3300 B.C.) (Saffirio 1972). J. R. Geller (1992) identified a brewery at Hierakonpolis by examining the chemistry of the black residue found in the brewery vats dating from roughly the same time. Similar beer vat sites have been discovered in Egypt from the Amratian (about 3800-3500 B.C.) through the Early Dynastic period (about 3100-2686 B.C.) (Geller 1989).
A yeast, resembling modern Saccharomyces spp. and named Saccharomyces winlocki, was found in an undisturbed Theban tomb of the Eleventh Dynasty (2135-2000 B.C.) (Gruss 1928). S. winlocki was also found in an amphora containing beer in the tomb of Queen Meryet-Amun of the Eighteenth Dynasty (1570-1305 B.C.) at Thebes (Winlock 1973).
The bag press, used to press grapes in the manufacture of wine, is shown on the walls of Egyptian tombs from around 3000 B.C. (Forbes 1967). Wine was drunk by upper-class Egyptians and beer was the beverage of the lower classes. Leavened bread was also a common food, as is illustrated by paintings in the tomb of Ramses III (Goody 1982).
According to H. A. Dirar (1993), date wine, beer, bread, and cake may have been made in the Sudanese Kingdom of Yam (2800-2200 B.C.). Two men drinking beer or wine through a bamboo straw are shown in a drawing at Mussawarat es Sufra, a site dating to Meroitic times (from between 1500 and 690 B.C. to A.D. 323). Strabo (7 B.C.) mentioned that the Meroites (Ethiopians) knew how to brew the sorghum beer that is called merissa today. Wine, which dated from between 1570 and 1080 B.C., was introduced into the Sudan by Egyptian colonists of the New Kingdom (Dirar 1993).
In Chinese folklore, Shen Nung, the “Divine Ploughman,” a mythical ruler, taught the people how to use plant medicines and, presumably, taught them about fungi as well. Y. C. Wang (1985) has suggested that the Chinese knew about fungi some 6,000 to 7,000 years ago but offered no specific evidence for their use as food. K. Sakaguchi (1972), who wrote that mold fermentation was traceable to about 1000 B.C. in China, has been supported by T. Yokotsuka (1985).
B. Liu (1958) claimed that in China, mushrooms were first eaten in the Chou Dynasty about 900 B.C. Lui Shi Chuen Zhou, in his Spring and Autumn of Lui’s Family, recorded the eating of ling gi (Ganoderma sp.) about 300 B.C. (Liu 1991). The Book of Songs, printed in the Han Dynasty (26 B.C. to A.D. 220), mentioned over 200 useful plants, including a number of common edible mushrooms (Wang 1985). Similarly, the Book of Rites, written about A.D. 300, mentions several edible fungi (Wang 1985).
Auricularia auricula and Auricularia polytrica (“wood ear”) were described by Hsiang Liu (about 300-200 B.C.) and by Hung Wing T’ao (between A.D. 452 and 536). The T’ang Pen Ts’ao of the Tang Dynasty (seventh century) described five kinds of mu-erh, which grew on various trees.The cultivation of the mushrooms (Auricularia spp.) was begun in the Tang Dynasty (A.D. 618-907) (Chang and Miles 1987), although they were probably eaten at least 1,400 years ago (Lou 1982).
The mushroom Lentinus edodes (shiitake) was recognized as the “elixir of life” by a famous Chinese physician, Wu Shui, during the Ming Dynasty (1368-1644). This was testimony to a primitive form of shiitake cultivation, called hoang-ko, that had been developed about 800 years ago (Ito 1978). According to R. Singer (1961), Japanese Emperor Chuai was offered the singular mushroom by the natives of Kyushu in A.D. 199, from which we may infer that they were gathered for consumption much earlier in China.
The Chinese method of producing alcoholic beverages required that Rhizopus, Mucor, or Saccharomyces spp. be grown spontaneously on compact bricks of wheat f lour or other materials called kyokushi. This process was said to have been introduced into Japan at the beginning of the fifth century A.D. and, hence, must have been used appreciably earlier in China (Kodama and Yoshizowa 1977).
A pigment from a fungus was mentioned in Jih Yang Pen Chaio (Daily Herb), written by Jui Wu in A.D. 1329. The organism producing the pigment was the yeast Monascus sp. (Wang 1985), which grows on rice and has been widely used in the Orient. It is the source of a red pigment employed to color such things as wine and soybean cheese (Lin and Iizuka 1982).
The Mongolian conquests introduced another source of fungal foods – cheese – to the Chinese people, who generally shunned dairy products. Su Hui, royal dietician during the reign of Wen Zong (Tuq. Temur) from A.D. 1328 to 1332, wrote Yenishan Zhengyao (The True Principles of Eating and Drinking). In it he included dairy products such as fermented mare’s milk, butter, and two cheeses (Sabban 1986).Another dietician of the Yuan Dynasty, Jia Ming (A.D. 1268-1374), also discussed the use of cheese over vegetables or pasta and mentioned fungi as food (Sabban 1986).
As previously hinted, cultivation (rather than gathering from the wild) of mushrooms for human food on a large scale may first have begun in China as early as the Han Dynasty (206 B.C. to A.D. 9). In the first century A.D.,Wang Chung’s Lun Heng stated that the cultivation of chih (fungus) was as easy as the cultivation of beans. In 1313, procedures for mushroom cultivation were described in Wong Ching’s Book of Agriculture (Chao Ken 1980).
Fermented protein foods have an ancient history in China (Yokotsuka 1985). According to the Shu-Ching, written about 3,000 years ago, chu (yeast or fungus) was essential for the manufacture of alcoholic beverages from wheat, barley, millet, and rice as early as the Chou Dynasty, 1121-256 B.C. By the Han Dynasty, chu was made in the form of a cake called ping-chu. A sixth-century text on agricultural technology, Chi-Min Yao Shu, detailed the preparation of several kinds of chu and other fermented foods such as chiang (fermented animal, bird, or fish flesh with millet). Chu was a common flavoring in the China of the Chou Dynasty (1121-256 B.C.), and chiang was mentioned in the Analects of Confucius, written some 600 years after that period. S. Yoshida (1985) wrote that fermented soybeans originated in China in the Han Dynasty and were known as shi.
Greece and Rome
That the ancient Greeks used fungi as food seems clear, because accidental mushroom poisoning was mentioned in the fifth century B.C. by both Euripides and Hippocrates (Buller 1914-16). Theophrastus (d. 287 B.C.) apparently knew and named truffles, puff-balls, and fungi (Sharples and Minter 1983).
The Romans enjoyed boleti (the Agaricus of today) and even had special vessels, called boletari, to cook the fungi (Grieve 1925). Presumably, a dish of boleti concealed the poisonous mushrooms that Agrippina administered to her husband, the Emperor Claudius, so that her son, Nero, could become emperor of Rome (Grieve 1925).
According to J. André (1985), the Romans ate Amanita caesarea, Boletus purpureus, and Boletus suillus, as well as truffles, puffballs, and morels (Rolfe and Rolfe 1925). Fungi must have been prized by wealthy Romans, for they are mentioned as special delicacies by Horace (65-8 B.C.), Ovid (43 B.C. to A.D. 19), Pliny (A.D. 46-120), Cicero (A.D. 106-143), and Plutarch (A.D. 46-120) (Rolfe and Rolfe 1925;Watling and Seaward 1976). The oldest cookbook presently known was written by Caelius Apicius in the third century A.D. and includes several recipes for cooking fungi (Findlay 1982).
The earliest reference to mushrooms in Japanese texts is in the Nihongi (Book of Chronicles), completed in A.D. 720, which recorded that mushrooms were presented to the Emperor Ojin in A.D. 288 by the local chieftains in Yamato (Wasson 1975). But according to Singer (1961), the earliest consumption of fungi in Japan was in A.D. 199, when the Emperor Chuai was offered shiitake by the natives of Kyushu. Mushrooms are rarely mentioned in the early poetry of Japan, but Manyoshu, the first anthology of poetry (compiled in the latter half of the eighth century), refers to the pine mushroom, and the Shui Wakashu (from about A.D. 1008) mentions it twice. In the Bunrui Haiku Zenshu, written by Masaoka Shiki sometime around the beginning of the sixteenth century, there were 250 verses about mushrooms and mushroom gathering (Blyth 1973).
The Spanish conquerors of Mexico reported in the sixteenth century that the Aztecs used a mushroom called teonanacatl (“god’s flesh”), and sacred mushrooms were pictured in the few Mayan manuscripts that survived the Spanish destruction of “idols and pagan writings.”The Mayan Codex Badianus, written in 1552 by Martin de la Cruz, an Indian herbalist, mentioned the use of teonanacatl for painful ailments. The Codex Magliabecchi (c. 1565) includes an illustration depicting an Aztec eating mushrooms, and Franciscan friar Bernardino de Sahagun (1499-1590) discussed, in his General History of the Things of New Spain, the use of teonanacatl to induce hallucinations (Guerra 1967). The Aztecs were familiar enough with fungi to give them names: nanacatl (mushroom), teonanacatl (sacred mushroom), and quauhtlanamacatl (wild mushroom). Indeed, the Mazatecs of Oaxaca and the Chinantecs of Mexico still use hallucinogenic mushrooms for divination, medical diagnosis, and religious purposes (Singer 1978).
The Near East
Al-Biruni, an Arab physician of about 1,000 years ago, described the eating of several fungi, including truffles (Said, Elahie, and Hamarneh 1973). Terfazia urenaria is the truffle of classical antiquity, and it is prized in the Islamic countries of North Africa and the Near East as terfaz. The best truff les were reputed to come from the areas of Damascus in Syria and Olympus in Greece (Maciarello and Tucker 1994).
Truffles were already a part of Roman cuisine by the first century A.D., when the Roman poet and satirist Decimus Junius Juvenalis wrote: “[T]he Truffles will be handed round if it is Spring, and if the longed-for thunders have produced the precious dainties.” At that time, fungi were thought to originate when lightning struck the earth during thunderstorms. Truffles were a part of French cuisine by the time of the Renaissance and were exported to England by the beginning of the eighteenth century (Maciarello and Tucker 1994).
In France, mushrooms were cultivated on manure from horse stables during the reign of Louis XIV (Tounefort 1707), and F. Abercrombie (1779) described an English method of composting such manure for the growth of mushrooms by stacking it, a method still in use today. Mushrooms are still highly prized as food in Europe. Many wild fungi are gathered and eaten, and many more are cultivated or imported (Mau, Beelman, and Ziegler 1994).
Fungi Eaten Now and in the Past by Humans
Fungi have been a prized food of peoples past and present around the world. Fungi are mostly eaten cooked, although some ethnic groups and individuals eat them raw. Today, the people of Asia appear to be the most eclectic consumers of fungi. The Chinese eat perhaps as many as 700 wild and domesticated species. The Japanese use well over 80 species (Imai 1938); the people of India may consume more than 50 species; and the French, not to be outdone, enjoy well over 200 species from one area alone – that of HauteSavoie (Ramain 1981). Similarly, North Americans eat more than 200 wild and cultivated fungal species (Lincoff 1984).
The reader should be aware that many mushroom genera include both edible and toxic species, and that some mushroom varieties can be edible, whereas others of the same species are not. In the case of some mushrooms, boiling in water before eating will remove toxic or unpleasant secondary metabolites.
Relatively barren areas of the Near East, including parts of Africa and Asia, support thriving populations of truffles, genus Tirmania, which are eaten from Morocco and Egypt in North Africa to Israel, Saudi Arabia, and Iraq (Said et al. 1973; Alsheikh, Trappe, and Trappe 1983). Truffles called fuga are prized in Kuwait and eaten with rice and meat (Dickson 1971). In some areas of the Arabian Gulf, the truffle crop may be appropriated by the local royal families (Alsheikh et al. 1983).
Today, edible fungi are cultivated or collected in the wild in huge numbers and shipped by air from the source country to consumer countries around the world; fungi may also be canned or dried for long-term storage and later consumption.
a ndiwa (Chichewa) or mboga (Yao) is a relish or side dish of mushrooms fried in oil with onions, tomatoes, and ground nut flour.
Gross Chemical Composition of Fungi
The gross chemistry of edible fungi varies with the stage of the life cycle in which they are eaten; for example, the mycelium of Agaricus campestris, a common white mushroom, contains 49 percent protein (Humfeld 1948), whereas the sporophore of the same species is 36 percent protein (McConnell and Esselen 1947).
Even the stage in the life cycle of the sporophore may significantly affect the gross chemistry of the fungus.The sporophore is the fungal part usually eaten, although the mycelium predominates in fermented foods (Purkayastha and Chandra 1976).
Most of the biomass of fungi is water, although there are wide variations in the amount of water in different species. The dry biomass is mainly carbohydrates, followed by proteins, lipids, and ash, in that order; again, there is wide variation in the amounts of the major components. In general, dried fungi contain 2 to 46 percent protein, 5 to 83 percent carbohydrates, 1 to 26 percent lipids, 1 to 10 percent RNA, 0.15 to 0.3 percent DNA, and 1 to 29 percent ash (Griffin 1981). Fungal strains with unusually high lipid content have been selected for this trait and are grown under conditions where lipid synthesis is enhanced. These fungi serve as valuable sources of lipids that are required in large quantities for industrial purposes.
The nutritional value of many edible fungi compares well with other common foods. In essential amino acid content, where meat rates 100 and milk 99, mushrooms are rated at 98. Measuring by amino acid “score,” meat scores 100, milk scores 91, and mushrooms score 89, whereas, by nutritional index, meat can score between 59 and 35, soybeans score 31, and mushrooms score 28. Indeed, by any of these criteria, some mushrooms have more nutritional value than all other plants except soybeans; at the same time, however, some edible fungi score much lower by the same criteria (Crisan and Sands 1978). One hundred grams of dried fungal biomass has an energy equivalent of from 268 to 412 kilocalories (Griffin 1981).
Soluble carbohydrates in fresh fungi range from 37 to 83 percent of the dry weight. In addition, there are fiber carbohydrates that make up from 4 to 32 percent (Griffin 1981).
The lipid content of fungi ranges from 0.2 percent of the cell or tissue dry weight to as high as 56 percent – more specifically, 0.2 to 47 percent for Basidiomycotina, and 2 to 56 percent for Deuteromycotina (Weete 1974; Wassef 1977). Sporophores’ contents of lipids tend to be relatively low, but among them are triglycerides, phospholipids, fatty acids, carotenoids, and steroids, as well as smaller amounts of rarer lipids.
Carotenoids may accumulate in some fungi; in fact, some pigmented fungi have been grown in bulk precisely for carotenoids, which are fed to carp or to chickens to color their eggs and make them more acceptable to the consumer (Klaui 1982). Some of these carotenoids may be converted to vitamin A in humans (Tee 1992).
In addition, some fungi are sufficiently good producers of the B vitamins to make them viable commercial sources of these nutrients. Saccharomyces spp., for example, are good sources of B vitamins generally (Umezawa and Kishi 1989), and riboflavin is obtained in goodly amounts from Ashbya gossppii fermentations (Kutsal and Ozbas 1989).
Fungal Flavors and Volatiles
The nonvolatile meaty flavors of edible fungi come primarily from the amino acids (glutamic acid is one of the most common), purine bases, nucleotides (such as the shiitake mushroom’s guanosine-5 • -monophosphate) (Nakajima et al. 1961), and the products of the enzymatic breakdown of unsaturated fatty acids.The volatile flavors include C8 compounds, such as benzyl alcohol, benzaldehyde, and other compounds (Mau et al. 1994). Many fungi contain monoterpenes, which produce a variety of flavors and odors; Trametes odorata, Phellinus spp., andKluyveromyces lactis, for example, produce linalool (sweet, rose-like), geraniol (rose-like), nerool (sweet, rose-like) and citronellol (bitter, rose-like).
Fungi also produce flavors and odors that are buttery; nutlike; mushroomlike; coconut-like (Trichoderma spp.); peachlike (Fusarium poae, Pityrosporium spp., Sporobolomyces odorus, Trichoderma spp.); flowery and woody (Lentinus lepideus); earthy (Chaetomium globosum); sweet, aromatic, and vanilla-like (Bjerkandera adusta); coconut- and pineapple-like (Polyporus durus); sweet and fruity (Poria aurea); and passion-fruit-like (Tyromyces sambuceus) (Kempler 1983; Schreier 1992).
The flavor of truffles, as in other fungi, is partly caused by nonvolatile organic molecules such as those mentioned previously and by over 40 volatile organic molecules.The aroma of white truffles comes mainly from one of the latter, whereas the Perigord (black) truffle’s aroma is the result of a combination of molecules. Species of Russula, when dried, have an odor that has been attributed to amines (Romagnesi 1967).
Some fungi produce volatile molecules that attract animals – including humans – or emit distinct flavors (Schreier 1992). Truffles, which are among the most valuable of edible fungi, grow underground on plant roots and produce odors that can only be recognized by dogs, pigs, and a few other mammals. Humans cannot smell them, but those with experience can detect the presence of truffles below the ground by cracks that appear in the soil surface over the plant roots.
The major species of truffles are Tuber melanosporum – the black truffle or so-called Perigord truffle – found most frequently in France, Italy, and Spain; Tuber brumale, also of Europe; Tuber indicum of Asia; and Tuber aestivum – the summer truffle or “cook’s truffle” – which is the most widespread of all the truff les and the only one found in Britain (Pacioni, Bellina-Agostinone, and D’Antonio 1990).
Fungi and Decay
Along with bacteria, fungi hold primary responsibility for the biological process known as decay, in which complex organic molecules are progressively broken down to smaller molecules by microbial enzymes.The decay process destroys toxic molecules and regenerates small molecules used by microbial or plant life. Examples include carbon as carbon dioxide and nitrogen as amino acids, nitrates, or ammonia. Dead plants and animals are broken down to humus and simpler organic molecules that fertilize the soil and increase its water-holding capacity.These same processes have been used by humans in fermentation and in the production of bacterial and fungal single-cell protein (SCP) from waste or cheap raw materials.
The process of fermentation or microbial processing of plant or animal foods has served many functions, both now and in the distant past, especially in warm and humid climates where food spoils quickly. Fermentation preserves perishable food at low cost, salvages unusable or waste materials as human or animal food, reduces cooking time and use of fuel, and enhances the nutritional value of food by predigestion into smaller molecules that are more easily assimilated. Sometimes, but not always, fermentation increases the concentration of B vitamins (Goldberg and Thorp 1946) and protein in food (Cravioto et al. 1955; Holter 1988) and destroys toxic, undesirable, or antidigestive components of raw food. Moreover, fermentation can add positive antibiotic compounds that destroy harmful organisms, and the acids and alcohol produced by fermentation protect against microbial reinfection and improve the appearance, texture, consistency, and flavor of food. In addition, fermented foods often stimulate the appetite (Stanton 1985).
In ancient times, preservation of foods (such as milk, cheese, and meat) and beverages (like beer, mead, and wine) by fermentation made it possible for humans to travel long distances on land or water without the need to stop frequently for water or food. As described by Dirar (1993), over 80 fermented foods and beverages are presently used by the people of the Sudan, including 10 different breads, 10 different porridges, 9 special foods, 13 different beers, 5 different wines, 1 mead, 7 dairy sauces, 4 different meat sauces, 5 different fish sauces, 5 flavors and substitutes of animal sauces, and 10 flavors and substitutes of plant origin.
Today a wide variety of mainly carbohydrate-rich substrates, like cereals, are preserved, but protein-rich legumes and fish can also be processed by fungi. The combination of fungi, yeast, and bacteria is often controlled by antibacterials, fatty acids that act as trypsin inhibitory factors, and phytases, which destroy soybean phytates that bind essential metals (Hesseltine 1985).
Fungal fermentation of cereals does not lead to a marked increase in the protein content of the grain, but it does contribute to a significant increase in amino acids, especially those considered essential to humans. There is a decrease in carbohydrates during fungal fermentation, and lipids are hydrolyzed to fatty acids. Fungal fermentation may lead to an increase in B-vitamin content, although B12 will appear only if bacteria are involved in the fermentation.
Soybeans constitute a good example. Normally they contain B vitamins, but neither vitamin B12 nor significant amounts of proteins. When fermented, however, the B vitamins (except for thiamine) increase, and proteins are completely hydrolyzed to amino acids (Murata 1985). Vitamin B12 has been found in all commercial samples of fermented tempe, indicating that bacteria were involved in the fermentation as well (Steinkraus 1985).
In Fiji, carbohydrate-rich crops such as breadfruit (Artocarpus utilis), cassava (Manihot dulcis), taro (Colocasia esculenta), plaintain (Musa paradisiaca subsp. normalis), banana (Musa subsp. sapientum), and giant swamp taro (Alocasia indica) are preserved for future use by pit-mixed fermentation. This process was probably brought to Tonga during the Lapita period some 2,000 to 3,000 years ago and subsequently spread to Fiji (Aalbersberg, Lovelace Madhaji, and Parekenson 1988).
Single-Cell Protein for Human and Animal Food
Fungi have been employed to produce single-cell protein (SCP) from a variety of waste materials that might otherwise be useless, such as crop straw, bagasse, starchy plant materials, and whey, among others. Candida alkane yeasts have been examined for their ability to produce protein-rich biomass and edible calories for pigs and other animals, whereasChaetoceros and Sporotrichum spp. have been utilized to enrich the protein content of lignocellulose wastes – like straw – for animal feed. Rhizopus oligosporus NRRL 270 has been used to increase the protein content of starchy residues (cassava, potato, and banana), and yeasts have been exploited to produce food and alcohol from whey. Treating manioc with R. oligosporus by any of three different fermentation methods has resulted in a marked increase in protein content, seemingly at the expense of the carbohydrate content of the manioc (Ferrante and Fiechter 1983).
In Europe, the Near East, and South and Central America, saccharification of the starch in cereals – such as barley, corn, or wheat – has long been done by malting the grain. This procedure is followed by the production of alcoholic beverages and food through the action of Saccharomyces spp. In the Orient, Aspergillus spp. and Rhizopus spp. remain in use to make alcoholic beverages and foods, and the same two fungal species are also employed to hydrolyze the proteins of fish, meat, beans, pulses, and some cereals.
Other Fungally Fermented Foods
Some cheeses are made flavorful – following the formation of the curd and its processing – through the action of enzymes of the fungi Penicillium camembert (Camembert and Brie) and Penicillium roqueforti (Bleu, Gorgonzola, Roquefort, and Stilton). Country-cured hams are produced through fermentation by Aspergillus and Penicillium spp.; tuna is fermented by Aspergillus glaucus, cocoa by Candida krusei and Geotrichum spp., and peanut presscake by Neurospora sitophila(Jay 1986).
Fungal Secondary Metabolites
Fungi produce a large variety of secondary metabolites, but often only when the fungal cells cease active growth. Some of these secondary metabolites are beneficial to humans, whereas others are toxic, and still others may have useful medical effects.
Fungi supply organic acids for industrial uses: citric acid for the food, beverage, pharmaceutical, cosmetic, and detergent industries; itaconic acid for the plastic, paint, and printer’s-ink industries; fumaric acid for the paper, resin, fruit juice, and dessert industries (Bigelis and Arora 1992; Zidwick 1992); gluconic acid for the food, beverage, cleaning, and metal-finishing industries; and malic and lactic acids for the food and beverage industries. In addition, several fungi produce rennets for the dairy industry; among these are Byssochlamys fulva, Candida lipolytica, Chlamydomucor oryzae, Flammulina velutipes, Rhizopus spp., and Trametes ostreiformis (Sternberg 1978).
Certain fungi (especially Streptomyces spp.) have proven to be useful as sources of a host of antibiotics that act as inhibitors of bacterial cell-wall synthesis (Oiwa 1992), as antifungal agents (Tanaka 1992), as antiviral agents (Takeshima 1992), and as antiprotozoal and anthelminthic agents (Otoguro and Tanaka 1992). Some also produce antitumor compounds (Komiyama and Funayama 1992), cell-differentiation inducers (Yamada 1992), enzyme inhibitors (Tanaka et al. 1992), immunomodulation agents (Yamada 1992), and vasoactive substances (Nakagawa 1992). In addition, fungi have been used to produce herbicides (Okuda 1992), fungicides, and bactericides of plants (Okuda and Tanaka 1992).
A number of secondary metabolites of fungi, however, are toxic to humans and their domestic animals. Aflatoxins are hepatotoxic and carcinogenic; deoxynivalenol is emetic; ergot alkaloids are vasoconstrictive, gangrenous, hemorrhagic, and neurotoxic; zearalenone causes vulvovaginitis in swine; trichothecenes produce vomiting, oral necrosis, and hemorrhage; ochratoxin causes nephrotoxicity; and macrocyclic trichothecenes cause mucosal necrosis (Marasas and Nelson 1987).
Those species of the fungal genus Claviceps that grow on cereals (as for example, Claviceps purpurea) produce a variety of pharmacologically active compounds with positive and negative effects on humans. Among these are the alkaloids lysergic acid diethylamide (LSD), ergometrine, ergotrienine, ergotamine, ergosinine, ergocristine, ergocornine, ergocristinene, ergocryptine, and ergocryptinine. Some of these alkaloids are responsible for the disease ergotism, but others are used beneficially – in childbirth, or to treat migraines (Johannsson 1962).
Still other fungi associated with cereals and legumes produce a wide variety of toxins.These have been implicated in aflatoxin and liver cancer in Africa, in esophageal cancer in Africa and Asia, and in endemic nephritis in the Balkans (Stoloff 1987).
A number of fungi (i.e., Fusarium and Gibberella spp.) produce zearalanol, which exhibits estrogen activity. These estrogen-like compounds are frequent contaminants in cereals and may be responsible for carcinogenesis and precocious sexual development if present in quantity (Schoental 1985).
Aspergillus flavus, which grows on peanuts, soybeans, cereals, and other plants, may produce the hepatocarcinogen aflatoxin and can cause Reye’s syndrome in children. Fusarium spp., also growing on cereals, can produce trichothecen toxins that cause toxic aleukia (ATA) and akakabi-byo (“red mold disease”) in Japan.
The commonly cultivated mushroom, Agaricus bisporus, may contain phenylhydrazine derivatives that have been found to be weakly mutagenic. Many other edible fungi have shown mutagenic activity (Chauhan et al. 1985); among them is the false morel, Gyrimitra esculenta, which has been found to contain 11 hydrazines, including gyromitrin – and 3 of these hydrazines are known mutagens and carcinogens (Toth, Nagel, and Ross 1982; Ames 1983; Meier-Bratschi et al. 1983).
In addition, a number of wild fungi contain poisonous molecules that can cause serious illness or death. The amount of poison varies from species to species and from strain to strain within individual species (Benedict and Brady 1966). Also, humans vary in their tolerance of fungal poisons (Simmons 1971).
Fungal toxins produce a variety of biological effects: Amanitin, phallotoxins, and gyromitrin cause kidney and liver damage; coprine and muscarine affect the autonomic nervous system; ibotenic acid, muscimol, psilocybin, and psilocin affect the central nervous system and cause gastrointestinal irritation; indeed, many of these substances and other unknown compounds found in fungi are gastrointestinal irritants (Diaz 1979; Fuller and McClintock 1986).
Several edible fungi, such as Coprinus atramentarius, Coprinus quadrifidus, Coprinus variegatus, Coprinus insignis, Boletus luridus, Clitocybe clavipes, and Verpa bohemica, may contain coprine (Hatfield and Schaumburg 1978). Indeed, European C. atramentarius may have as much as 160 mg of coprine per kg of fresh fungi. In the human body, coprine is hydrolyzed to l-aminocyclopropanol hydrochloride (ACP), which acts like disulfuram, a synthetic compound known as antabuse and used to treat chronic alcoholics. Antabuse and ACP irreversibly inhibit acetaldehyde dehydrogenase and prevent the catabolism of ethanol. Thus, coprine plus ethanol leads to severe intoxication when alcoholic beverages are drunk after eating coprine-containing fungi (Hatfield and Schaumberg 1978; Hatfield 1979).
In addition, many mushrooms contain the enzyme thiaminase, which may destroy the vitamin thiamine, leading to thiamine deficiency (Wakita 1976) – especially when the mushrooms are eaten in quantity (Rattanapanone 1979). Several Russula spp. may contain indophenolase, which can also be harmful to humans if eaten in large amounts (Romagnesi 1967).
Humans can become allergic to fungi (Koivikko and Savolainen 1988). Moreover, eating fava beans with mushrooms that are rich in tyrosinase may enhance the medical effect of the fava beans – known as favism – because the tyrosinase catalyzes the conversion of L-DOPA to L-DOPA-quinone (Katz and Schall 1986).
Magico-Religious Use of Fungi
As early as the eighteenth century, according to travelers’ reports, Amanita muscaria, known as the “fly agaric,” was eaten by several tribal groups (Chukchi, Koryak, Kamchadal, Ostyak, and Vogul) in eastern Siberia as an intoxicant and for religious purposes. Species of Panaeolus, Psilocybe, and Stropharia also contain hallucinogens.These fungi were eaten by the Aztecs and the Maya – and are still consumed by curanderos in some Mexican tribes – to produce hallucinations for religious purposes, to derive information for medical treatment, and to locate lost objects (Diaz 1979).